|
%I #23 Jul 16 2022 07:14:24
%S 1,4,8,9,12,15,16,18,20,24,25,27,30,32,33,35,36,40,42,44,45,48,49,50,
%T 54,55,56,60,63,64,65,66,69,70,72,75,77,78,80,81,84,87,88,90,91,92,96,
%U 98,99,100,104,105,108,110,112,115,116,117,119,120,121,123
%N Numbers k such that phi(1)*phi(2)*...*phi(k) / k is an integer, where phi(k) is the totient function (A000010).
%H Amiram Eldar, <a href="/A145190/b145190.txt">Table of n, a(n) for n = 1..10000</a>
%t Select[Range[200], IntegerQ[Product[EulerPhi[i], {i, 1, #}]/#] &] (* _Carl Najafi_, Aug 19 2011 *)
%t nn=150;With[{ep=Rest[FoldList[Times,1,EulerPhi[Range[nn]]]]}, Flatten[ Position[Table[ep[[i]]/i,{i,nn}],_?IntegerQ]]] (* _Harvey P. Dale_, May 12 2012 *) (* this program is more than 200 times faster than the first Mathematica program above *)
%o (PARI) isok(n)=prod(k=1,n,eulerphi(k))%n==0 \\ _Anders Hellström_, Aug 22 2015
%Y Cf. A000010, A048290, A144857.
%K easy,nonn
%O 1,2
%A _Ctibor O. Zizka_, Oct 03 2008
%E More terms from _Carl Najafi_, Aug 19 2011
|
